You can't go on maternity any earlier but you may be able to be be signed off by your GP until your mat leave starts if you feel you can't work x
Can’t give advice about maternity leave but I’m a hairdresser too (also have a 3 year old to run after 🥴😂) and have a killer back so spoke to my midwife and she’s ordered me a support band - have you tried anything like that yet?
I think you can only start it from 11 weeks before your due date but could go to the doctor's and get them to write you off sick and take sick leave until your maternity leave can start x